Flexible, collapsible containers or bags made of plastic have achieved very significant commercial acceptance in the field of parenteral solution and blood bags. Initially, these items have been made from heat-sealed vinyl plastic sheets, and have been quite satisfactory. However, it has been recognized that significant costs can be saved by the use of other manufacturing procedures such as blowmolding and the like. Also, there has been consideration of the use of less expensive materials other than vinyl plastic in containers, particularly those materials that do not contain a plasticizer. For example, polypropylene has been considered a suitable candidate for use as a container material, when extruded as a thin, flexible sheet.
However, it has proven difficult to manufacture thin-walled plastic bags from polypropylene which are capable of collapsing, yet which are strong enough to stand rough handling without breaking. For example, when many filled, conventional designs of blow-molded, polypropylene bags are dropped on the floor, they rupture along their tail seal line, which is the point at which the tubular plastic parison, from which the container is made by blow molding, is sealed together at its end.
One reason for this weakness is that, even if the flexible bag or container material is oriented by some process such as the well-known Orbet process of the Phillips Petroleum Company of Bartlesville, Oklahoma, the seal area at the end of the bag remains unoriented, and thus is not as strong as the rest of the bag.
Accordingly, there is a need for a stronger thin-walled, collapsible container or bag for use in dispensing blood, parenteral solutions, or any other desired material, which can be made by a blow-molding process or another automated, cost-saving method, and which can be made from plasticizer-free materials such as polyethylene, polypropylene, or other similar plastic materials.
In accordance with this invention, an improved seal structure for flexible-walled containers is disclosed, which may be used with either oriented or non-oriented plastic containers, resulting in a more reliable sealed end for such containers, especially for blow-molded containers made from tubular plastic parisons.